System and method for monitoring esophagus proximity

ABSTRACT

A system for determining the proximity of the esophagus to the ablation electrode of an ablation catheter during an ablation procedure is disclosed. The system comprises an ablation catheter having at least one ablation electrode, an esophageal probe catheter having at least one electrode, and a signal processing unit. Both the ablation electrode and the esophageal probe catheter are electrically connected to the signal processing unit. The signal processing unit receives electrical signals from the ablation electrode on the ablation catheter and the electrode on the esophageal probe catheter and compares the signals to determine the proximity of the esophagus to the ablation electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/236,278, filed Sep. 26, 2005, now U.S. Patent Publication No.2007-0106287, the entire contents of which are incorporated herein byreference.

FIELD OF THE INVENTION

This invention is directed to a system and method for measuring theproximity of the esophagus to the heart, in particular, the proximity ofthe esophagus to an endocardial catheter in use in the heart.

BACKGROUND OF THE INVENTION

Cardiac arrhythmias, and atrial fibrillation in particular, persist ascommon and dangerous medical ailments, especially in the agingpopulation. In patients with normal sinus rhythm, the heart, which iscomprised of atrial, ventricular, and excitatory conduction tissue, iselectrically excited to beat in a synchronous, patterned fashion. Inpatients with cardiac arrhythmias, abnormal regions of cardiac tissue donot follow the synchronous beating cycle associated with normallyconductive tissue as in patients with normal sinus rhythm. Instead, theabnormal regions of cardiac tissue aberrantly conduct to adjacenttissue, thereby disrupting the cardiac cycle into an asynchronouscardiac rhythm. Such abnormal conduction has been previously known tooccur at various regions of the heart, such as, for example, in theregion of the sino-atrial (SA) node, along the conduction pathways ofthe atrioventricular (AV) node and the Bundle of His, or in the cardiacmuscle tissue forming the walls of the ventricular and atrial cardiacchambers.

Cardiac arrhythmias, including atrial arrhythmias, may be of amultiwavelet reentrant type, characterized by multiple asynchronousloops of electrical impulses that are scattered about the atrial chamberand are often self propagating. Alternatively, or in addition to themultiwavelet reentrant type, cardiac arrhythmias may also have a focalorigin, such as when an isolated region of tissue in an atrium firesautonomously in a rapid, repetitive fashion.

Several pharmacological approaches intended to remedy or otherwise treatatrial arrhythmias have been disclosed, although such pharmacologicalsolutions are not generally believed to be entirely effective in manycases, and may in some cases result in proarrhythmia and long terminefficacy. Several surgical approaches have also been developed withthe intention of treating atrial fibrillation. One particular example isknown as the “maze procedure.” In general, the maze procedure isdesigned to relieve atrial arrhythmia by restoring effective atrialsystole and sinus node control through a prescribed pattern of incisionsabout the tissue wall. In the early clinical experiences reported, themaze procedure included surgical incisions in both the right and theleft atrial chamber. However, more recent reports predict that thesurgical maze procedure may be substantially efficacious when performedonly in the left atrium.

Success with surgical interventions through atrial segmentation,particularly with regard to the surgical Maze procedure, has inspiredthe development of less invasive catheter-based approaches to treatatrial fibrillation through cardiac tissue ablation. Examples of suchcatheter-based devices and treatment methods have generally targetedatrial segmentation with ablation catheter devices and methods adaptedto form linear or curvilinear lesions in the wall tissue which definesthe atrial chambers, such as those disclosed in U.S. Pat. No. 5,617,854to Munsif, U.S. Pat. No. 4,898,591 to Jang, et al., U.S. Pat. No.5,487,385 to Avitall, and U.S. Pat. No. 5,582,609 to Swanson, thedisclosures of which are incorporated herein by reference. The use ofparticular guiding sheath designs for use in ablation procedures in boththe right and left atrial chambers are disclosed in U.S. Pat. Nos.5,497,774, 5,497,119, 5,564,440 and 5,575,766 to Swartz et al., thedisclosures of which are incorporated herein by reference. In addition,various energy delivery modalities have been disclosed for forming suchatrial wall lesions, and include use of microwave, laser and morecommonly, radiofrequency energies to create conduction blocks along thecardiac tissue wall, as disclosed in International Publication No. WO93/20767 to Stern, et al., U.S. Pat. No. 5,104,393 to Isner, et al. andU.S. Pat. No. 5,575,766 to Swartz, et al., respectively, the disclosuresof which are incorporated herein by reference.

Ablation is most effectively performed when the distal tip electrode isin contact with the cardiac wall. Absence of contact or poor contact ofthe tip electrode with the heart wall leads to dissipation of the RFenergy in the blood, as well as possible fouling of the tip electrodewith the concomitant possibility of blood clot formation. Accordingly,it is important that both mapping and ablation be accompanied by methodsand systems for detecting and ensuring electrode-tissue contact. Anumber of references have reported methods to determine electrode-tissuecontact, including U.S. Pat. Nos. 5,935,079; 5,891,095; 5,836,990;5,836,874; 5,673,704; 5,662,108; 5,469,857; 5,447,529; 5,341,807;5,078,714; and Canadian Patent Application 2,285,342. A number of thesereferences, e.g., U.S. Pat. Nos. 5,935,079, 5,836,990, 5,447,529, and6,569,160 determine electrode-tissue contact by measuring the impedancebetween the tip electrode and a return electrode. As disclosed in the'160 patent, the entire disclosure of which is hereby incorporated byreference, it is generally known that impedance through blood isgenerally lower that impedance through tissue. Accordingly, tissuecontact has been detected by comparing the impedance values across a setof electrodes to pre-measured impedance values when an electrode isknown to be in contact with tissue and when it is known to be in contactonly with blood.

The success of catheter based ablation procedures has led to numerousimprovements to the catheters used for the procedures. However, thetraumatic nature of the ablation procedure has given rise to certaincomplications. One such complication is the possibility of damaging theesophagus, which lies very close to, and often touches the outer wall ofthe left atrium. Damage to the esophagus is sometimes caused when theesophagus touches or is close to the tissue in the left atrium that isbeing ablated. The heat from the ablation procedure may penetratethrough the tissue of the left atrium and reach the esophagus. Thisdamage to the esophagus is extremely dangerous, as the damaged esophagusoften becomes infected. Due to this infection, an esophageal fistula, orhole in the esophagus, develops over time, causing the infection tospread to the heart wall. This damage to the esophagus carries anextremely high mortality rate.

To avoid damage to the esophagus, a need exists for a method of locatingthe esophagus during catheter-based procedures within the heart, such asmapping and/or ablation. To that end, some physicians have used standardmapping catheters to record the pre-procedure location of the esophagus.However, such a pre-procedure location determination fails to accountfor the mobile nature of the esophagus. The esophagus generally does notremain stationary. Rather, the esophagus often moves back and forth suchas when the patient swallows or coughs, thereby positioning itself indifferent locations relative to the heart wall. As such, the esophagusmay change its location during a catheter-based endocardial procedure.The pre-procedure determination fails to account for this movement.Accordingly, a need exists for a method of locating the esophagus duringmapping and/or ablation procedures.

SUMMARY OF THE INVENTION

The present invention is directed to a system for continuouslymonitoring proximity between a catheter in a patient's heart and hisesophagus, by placing a second catheter in the patient's esophagus andmonitoring the proximity between the two catheters. The systemcontinuously applies proximity interpretation to a measuredcharacteristic of a proximity signal and is adapted to provide to theuser of the heart catheter an audio and/or visual signal indicative ofthe proximity and alert when the heart catheter is too close to theesophagus. The system monitors the proximity in real time while theheart catheter is in use in the heart for mapping and/or ablation tominimize the risk of the heart catheter perforating or burning theesophagus.

The system includes an endocardial or heart catheter positioned in aheart of the patient and an esophagus catheter positioned in theesophagus of the patient. A proximity signal is transmitted between thecardiac catheter and the esophagus catheter and a signal processing unitcompares signals from the two catheters to determine and monitor theproximity between the two catheters. In one embodiment, where thecatheters are separated by a distance, the signal processing unitprocesses the proximity signal transmitted by one of the catheters andreceived by the other of the catheters to detect a change in acharacteristic of the signal for determining a change in the distancebetween the catheters. Possible characteristics can be impedance, signalamplitude or signal phase.

In another embodiment, a system for monitoring proximity between acardiac catheter and an esophagus of a patient, includes a cardiaccatheter equipped with a location sensor detecting location signals thatare processed by a first processor to determine location of the heartcatheter. An esophagus catheter is positioned in the esophagus of thepatient at a distance from the cardiac catheter. A second processor isprovided to process the proximity signal transmitted by one catheter andreceived by the other catheter to detect a change in the distancebetween the catheters.

The esophagus catheter includes an elongated catheter body having adistal region, and at least one lumen therethrough. In one embodiment,there is at least one electrode mounted on the distal region adapted forelectrical communication of a proximity signal with the cardiaccatheter, and the distal region of the esophagus catheter is adapted toextend in the esophagus generally behind a left atrium of the patient'sheart. The esophagus catheter can also include a plurality of ringelectrodes adapted to receive a proximity signal, a temperature sensorand/or an electromagnetic location sensor.

The present invention includes a method of monitoring proximity betweena heart catheter positioned in a patient's heart and the patient'sesophagus, by positioning an esophagus catheter in the patient'sesophagus, transmitting a proximity signal between esophagus catheterand the heart catheter, and monitoring a characteristic of the proximitysignal responsive to a change in the distance between the catheters.

Nonlimiting examples of suitable analysis techniques for use with theaforementioned system, device and method include impedance measurement,pacing signal amplitude measurement, use of a magnetic field, use ofHall effect sensors, inductance measurement, and capacitancemeasurement. The present invention allows a physician to continuouslymonitor, throughout an entire mapping and/or ablation procedure, theposition of the esophagus relative to the catheter in use in the heart.This continuous, real time monitoring of the general location of theesophagus accounts for the mobility of the esophagus and substantiallydecreases the risk of damage to the esophagus.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic representation of a system according to oneembodiment of the present invention;

FIG. 2 is a schematic representation of a system according anotherembodiment of the present invention;

FIG. 3 a is a side cross-sectional view of the proximal end of thecatheter body of an esophageal probe catheter according to oneembodiment of the present invention;

FIG. 3 b is a longitudinal cross-sectional view of the proximal end ofthe catheter body of the esophageal probe catheter of FIG. 3 a, takenalong line 3 b-3 b;

FIG. 3 c is a side cross-sectional view of the distal end of thecatheter body of the esophageal probe catheter of FIG. 3 a;

FIG. 4 is a perspective view of an ablation catheter according to oneembodiment of the present invention;

FIG. 5 is a side cross-sectional view of the catheter body of theablation catheter of FIG. 4;

FIG. 6 a is a side cross-sectional view taken of the side opposite thatof FIG. 5 of the tip section of the ablation catheter of FIG. 5,including the junction between the catheter body and tip section;

FIG. 6 b is a longitudinal cross-sectional view of the tip section ofthe ablation catheter of FIG. 5, taken along line 6 b-6 b.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, the present invention provides an esophagusproximity measurement system S for continuously monitoring proximitybetween an endocardial or heart catheter in a patient's heart and hisesophagus by detecting and monitoring proximity between the heartcatheter and an esophagus catheter in the patient's esophagus. In anembodiment of the system S, as shown in FIG. 1, a heart catheter HC ispositioned in the heart, e.g., the left atrium, and an esophagus probecatheter EC is positioned in the esophagus generally posterior of theheart catheter HC. In accordance with the present invention, the systemS monitors in real time a separation or distance between the twocatheters to provide an indication of their relative position forpurposes of monitoring proximity between the heart catheter and theesophagus of the patient so as to avoid the heart catheter coming intoundesirable close contact with the esophagus and damaging the esophagus.An audio and/or visual signal representative of the proximity (or changethereof) is provided to an operator while the heart catheter HC is inthe patient and particularly while in use during a procedure such asmapping and/or ablation of left atrium 11. By monitoring the relativeposition of catheters HC and EC, the operator can minimize, if notavoid, damage to wall 13 of the esophagus such as from burn orperforation by the heart catheter HC.

In the disclosed embodiment of FIG. 1, the system S includes a locationpad 22 that is placed under the patient, a communication (COM) unit 20that processes in real time location data of the catheter HC in thepatient's heart and electrophysiological data of the heart, such asLocal Activation Times (LATs). Coupled to the COM unit 20 is anonfluoroscopic catheter-based electroanatomical cardiac mapping system15 that uses the data processed by COM unit 20 to provide simultaneouselectrophysiological and spatial information and displays a 3-Dreconstruction of the mapped cardiac chamber. The system 15 includes aworkstation 16 (with a personal computer storing patient data and maps,a mouse and a keyboard), and a visual display 18 such as an LCD monitorto display the 3-D electroanatomical map.

The system S also includes an electrophysiologic (EP) junction box 30which processes electrical activity of heart chamber muscle as detectedby the catheter HC for recordation and display as electrograms on anelectrophysiologic (EP) recorder 32.

The system S further includes a signal processing unit (SPU) 34 toperform proximity interpretation by processing electrical signals thatare indicative of the proximity between the two catheters. Electricalsignals from both catheters HC and EC are referenced in real time toeach other to determine the proximity between the catheters. In theillustrated embodiment of FIG. 1, the SPU 34 has three connectors: afirst connector 33 for power supply 35, a second connector 37 for theesophagus catheter EC and a third connector 39 for the heart catheter HCvia a patient interface unit PIU which provides cabling connectionsbetween most if not all of the components of the system S.

Electrode signals from the heart catheter HC are transmitted to the SPU34 through the EP junction box 30 which splits the electrode signalsbetween the SPU 34 and the EP Recorder 32. The EP junction box 30therefore receives electrode signals from both catheters HC and EC andreferences in real-time one or more selected characteristics of theelectrode signals from the catheters that are responsive to changes inthe proximity, separation or distance between the catheters HC and EC,as discussed below in further detail.

In accordance with the present invention, a visual and/or audio signalrepresentative of the proximity (or change thereof) between thecatheters HC and EC is provided by an optical output 45 and/or an audiooutput 47. As such, the operator of the heart catheter HC, particularlyduring ablation and mapping procedures, can assess and be informed on areal-time basis the proximity between the heart catheter HC and theesophagus catheter EC to avoid damage to the wall 13 of the esophagus.

The heart catheter HC may be similar to an electrophysiologicaldeflectable catheter having a catheter tip that is mounted on a distalend of a catheter body where the catheter tip has a tip electrode 40 andseveral proximal ring electrodes 42 that enable recording of unipolar orbipolar signals representative of electrical activity of the heartchamber muscle, such as of the left atrium 11. In accordance with anembodiment of the present invention, one or more of the electrodes 42and preferably the tip electrode 40 are also adapted to transmit aproximity signal that travels through a posterior wall 14 of the leftatrium 11 and the superior wall 13 of the esophagus to reach theesophagus catheter EC, although it is understood by one of ordinaryskill in the art that alternate embodiments may adapt the ringelectrodes 42 to also sense proximity signal traveling from theesophagus EC and through the esophagus superior wall 13 and the leftatrium posterior wall 14.

Just proximal the tip electrode of the heart catheter HC is a locationsensor 44 that is embedded within the catheter which responds to themagnetic fields generated by the location pad 22 to determine locationof the heart catheter HC within the patient's heart.

For mapping a heart chamber, such as the left atrium, and creating anelectroanatomical map, the location pad 22 beneath the patient generatesexternal energy fields, for example three magnetic fields, that code amapping space around the heart chamber with both temporal and spatialdistinguishing characteristics. These fields contain information used toresolve the location and orientation of the location sensor 44 in thetip section of the heart catheter HC.

Magnetic field signals received by the location sensor 44 aretransmitted through the catheter HC via lead wires to the PIU 24 via theconnection 48. The PIU 24 transmits the location signals to the COM unit20 via connection 50 where the signals are amplified and filtered asappropriate. Data received from the location sensor 44 is processed bythe COM unit 20 to obtain location data of the tip of the catheter HC(for example, x, y and z coordinates and also pitch and roll and yaw).Accordingly, a 3-D map of the heart chamber geometry can be generatedusing a plurality or series of location data obtained by dragging orotherwise moving the distal tip of the heart catheter along the interiorof the heart chamber.

Local heart electrical activity signals detected by the ring electrodes42 of the heart catheter HC are transmitted through the catheter HC viaseparate lead wires to the PIU 24 via the connection 48. From the PIUthese signals are sent via connection 52 to the EP junction box 30 andrelayed to the EP recorder 32 via connection 54. The EP recorder 32records and displays the electrophysiologic data in the form on anelectrocardiograph.

The heart chamber muscle electrical activity detected by the heartcatheter are also transmitted to the COM unit 20 which serves as anelectrophysiologic signal processor by calculating local activationtimes (LATs). The LATs are transmitted via connection 60 to theworkstation 16 which generates a 3-D real-time electroanatomical map forviewing on the display 18. The map's electrophysiological informationmay be color coded and superimposed on the 3-D heart chamber geometrygenerated from the location mapping obtained by the location sensor ofthe heart catheter described hereinabove. Accordingly, an operatorviewing the display is provided with a 3-D graphical representation ofthe patient's heart that is color coded in regions to show differentLATs. For example, the color red represents shorter LATs and the colorpurple represents longer LATs. In a normal functioning heart, regionsclosest to the sinus node are red and regions farthest to the sinus nodeare purple. Using different activation zones in the cardiac chamber,different maps are constructed showing different activation sequences.Thus, in addition to viewing the electrocardiographs provided by the EPrecorder 32, the user has access to a 3-D color-coded graphicalrepresentation of the patient's LATs.

The system 15 may also include an actuator 62, e.g., a foot pedal, incommunication with the system that allows the user to accept or rejectdata points, or acquire data points LATs are calculated from the datarecorded with each point accepted. Each point provides location data andan ECG signal that when compared to the ECG signal of the referencecatheter (typically located in the patient CS vein) enables calculationof timing differences and the LAT]. The system 15 may also include aprinter 64 for printing the color-coded, 3-D graphical anatomical and/orelectrophysiological representation of the heart.

For proximity interpretation of the catheters HC and EC, the SPU 34receives and processes signals detected by electrodes 70 on theesophagus catheter EC and the electrodes 42 on the heart catheter HC.The catheters and the SPU 34 completes a circuit as an electrical signalconducts between the two catheters by traveling through the hearttissue, the esophagus tissue and body fluids between the two catheters.Taking into consideration the known electrical properties of such tissueand fluids, the SPU 34 references the electrical signals from bothcatheters to each other to determine the proximity there between.

Where the heart catheter HC is adapted for ablation, an ablation energysource 90 provides energy via connection 92 to the PIU 24 and theconnection 48 to the catheter HC. The ablation energy source may be RFin nature, cryogenic, ultrasonic or microwave, as understood by one ofordinary skill in the art.

In one embodiment, proximity interpretation performed by the SPU 34 isbased on impedance in the current through the catheters EC and HC, asgenerated by a signal generator 80 supplying a signal to, for example,the heart catheter HC. The signal, for example, an AC signal of 2 μAmpsat 50 kHz, is transmitted to the PIU 24 via connection 82 where thesignal is amplified using operational amplifiers and then applied to thetip electrode 40 of the heart catheter HC via the connection 48. Thesignal flows from the tip electrode 40 of the catheter HC through theposterior wall 14 of the left atrium 11 and the superior wall 13 of theesophagus and any fluids present along this path and is sensed by theelectrodes 70 on the catheter EC. Since the current is fixed and flowsthrough a relatively short distance encountering generally consistenttissue and fluid media with little, if any, resistance, the change inimpedance in the current between the two catheters is primarilyattributable to a change in the distance between the catheters. Voltagesat the electrodes 70 of the esophagus catheter EC and the tip electrode40 of the heart catheter HC are obtained and amplified by the SPU 34which includes a microprocessor programmed to take the measured voltagesand the respective fixed current outputs and apply Ohm's Law tocalculate the impedance. The impedance measured (or a change in theimpedance measured) can be displayed on the SPU 34 for reference by theoperator.

As the catheters HC and EC approach each other or otherwise come intoclose proximity of each other, a decrease in intercatheter impedancetriggers a visual and/or audio signal to the user via the outputs 45and/or 47 to caution that the heart catheter distal tip is close to theesophagus. As understood by one of ordinary skill in the art, the audioand/or visual outputs may, for example, be triggered when a thresholdproximity has been reached. Or, as another example, have an activationfrequency proportional to the intercatheter proximity.

In another embodiment, proximity interpretation may also be based on apacing signal sent by the SPU 34 to the esophagus catheter EC andtransmitted by the electrodes 70 to the tip electrode 40 of the heartcatheter HC. As the distance between the catheters change, amplitude ofthe pacing signal increases. As understood by one of ordinary skill inthe art, the activation and/or frequency of activation of theaudio/visual signal to the user can be dependent on a change in theamplitude or a threshold amplitude to alert the user that the heartcatheter tip is too close to the esophagus. Moreover, in alternativeembodiments of the invention, the system S may measure a temporal changein the proximity signal between the two catheter, such as monitoring thephase of the proximity signal, or even use inductive sensors (morepreferable for metal detection), capacitive sensors, and/or Hall Effectsensors. These sensors may be located in the tip or body of eithercatheter as appropriate or desired to provide the same function inmonitoring on a real-time basis the proximity of the catheters to eachother.

In view of the foregoing, it is further understood by one of ordinaryskill in the art that the signal for proximity measurement may betransmitted by either one catheter to the other catheter, as the presentsystem detects a change in a characteristic of the proximity signal inmonitoring the distance between the two catheters, whether thecharacteristic is impedance, amplitude or phase.

Under fluoroscopic guidance, or other suitable guidance means, the heartcatheter HC is introduced into the patient's body and heart throughappropriate vascular access and positioned inside the heart chamber.Additional heart catheters, such as a catheter 100 positioned in thecoronary sinus may be used as a reference catheter or external referencesensors may be used in locating the position of the heart catheter HC.The esophagus catheter EC is also introduced into the patient'sesophagus under fluoroscopy.

The catheter HC is dragged over the endocardium, sequentially acquiringthe location of its tip together with its electrogram while in stablecontact with the endocardium. The system S determines the location andorientation of the heart catheter by means of the COM unit 20 and thesystem 15. Thus, as the catheter HC is moved inside the heart, thesystem S analyses its location and presents it to the operator, thusallowing navigation without the use of fluoroscopy.

A local activation time at each site is determined from the intracardiacelectrogram as derived from detections by the electrodes on the cathetertip. The 3-D chamber geometry is reconstructed in real time by use ofthe set of location points sampled from the endocardium. On the basis ofthe various LATs, the map constructed shows the activation sequenceresulting from the time activation of different zones in the cardiacchamber. The activation map may be color-coded (e.g., red indicating theearliest and purple the latest activation) and is superimposed on the 3Dchamber geometry.

At any time during the foregoing procedures, proximity signals may besent by one catheter and received by the other catheter, with thesignals being processed by the SPU 34 to provide an audio and/or visualsignal to the operator on a real time basis indicating the proximitybetween the heart catheter HC (or its distal tip region bearing theelectrode(s)) and the esophagus catheter EC.

Where the application includes ablation, a baseline impedancemeasurement may be taken before ablation begins to represent, forexample, an ideal distance to be maintained between the two catheters.To that end, the SPU 34 can be adapted to measure and store a baselineimpedance against which subsequent proximity measurements are comparedto alert the operator when the catheters are too close to each other. Inaccordance with the invention, the operator can monitor the distancebetween the two catheters on a real-time basis and is alerted when theheart catheter HC is too close to the superior wall of the esophagus andcan therefore better avoid inadvertently burning the esophagus orperforating it or the wall of the left atrium.

The present invention also contemplates an esophagus proximity detectionsystem S′ which can operate without mapping or navigationalcapabilities, with heart and esophagus catheters that can be introducedinto and used in the patient entirely by fluoroscopy as appropriate. Asshown in FIG. 2, electrophysiologic data sensed by the electrodes 40 onan endocardial or heart catheter HC are transmitted to the PIU 24, theEP junction box 30 and then the EP recorder 32 where electrograms arestored and/or displayed. Where ablation is to be applied, the ablationenergy source 80 is connected to the PIU 24 to energize a tip electrode40. The esophagus catheter EC is connected to a dedicated signalprocessing unit SPU 34 which completes a circuit with the heart catheterHC via the EP junction box 30 and the PIU 24.

Proximity signals generated by the signal generator 80 are transmittedto the electrode 40 of the heart catheter via the connection 82, the PIU24 and the connection 48 and are conducted through the heart wall, theesophagus wall and fluids in between, reaching the electrodes 70 of theesophagus catheter EC. In processes similar to those described above,the SPU 34 processes and compares the signals from the catheters HC andEC and sends the appropriate activation signals to the optical and oraudio outputs 45 and 47.

It is understood by one of ordinary skill in the art that for theforegoing embodiments, the signals processed and compared by the SPU 34to determine proximity are preferably those measured at the electrodelocations for improved accuracy. Signals measured from another locationmay reflect environmental differences such as different tissues anddifferent fluids that may alter the characteristic measured by the SPU34.

For the foregoing embodiments, the heart catheter may be similar to anelectrophysiological deflectable catheter having a tip electrode andseveral proximal ring electrodes. The catheter may be adapted formapping and/or ablation. Nonlimiting examples of suitable ablationcatheters for use as the heart catheter HC with tip electrodes and/orablation assemblies include those described in U.S. Pat. Nos. 6,733,499,6,477,396, 6,475,214 and 6,371,955, the entire disclosures of which areincorporated herein by reference. Nonlimiting examples of suitablemapping catheters for use as the heart catheter HC are described in aPCT application filed in Israel on Jan. 8, 1997, by applicant “Biosense”and titled “Mapping Catheter”, the disclosure of which is incorporatedherein by reference. One exemplary heart catheter is depicted in FIGS.4, 5, 6 a and 6 b, the components of which are described in general inthe aforementioned U.S. Pat. Nos. 6,733,499, 6,477,396, 6,475,214,6,371,955, and in the PCT application filed in Israel on Jan. 8, 1997,by applicant “Biosense” and titled “Mapping Catheter.”

Moreover, a system 15 for cardiac mapping and navigation may be a CARTOsystem, available from Biosense (Israel) LTD., Tirat Hacarmel, Israel,for determining the position of a catheter. Suitable electromagneticsensors for use with the present invention are described, for example,in U.S. Pat. Nos. 5,558,091, 5,443,489, 5,480,422, 5,546,951 and5,391,199, the entire disclosures of which are incorporated herein byreference

The illustrated embodiment of the esophagus catheter EC of FIG. 1,generally comprises an elongated catheter body 112 having proximal anddistal ends, and a distal region 114 that is configured to extend intothe esophagus. On the distal region, there may be mounted a plurality ofelectrodes 70 and a distal tip electrode 71.

With reference to FIG. 3, the catheter body 112 comprises an elongatedtubular construction having a single, axial or central lumen 118. Thecatheter body 112 is flexible, i.e., bendable, but substantiallynon-compressible along its length. The catheter body 112 can be of anysuitable construction and made of any suitable material. One exemplaryconstruction comprises an outer wall 120 made of polyurethane or PEBAX.The outer wall 120 may also be made of a suitable silicone containingmaterial. The outer wall 120 comprises an embedded braided mesh ofstainless steel or the like to increase torsional stiffness of thecatheter body 112 so that, when the proximal portion of the body 112 isrotated, portion of the catheter body 112 distal thereto will rotate ina corresponding manner.

The outer diameter of the catheter body 112 is not critical, but ispreferably no more than about 8 french, more preferably about 7 french.Likewise, the thickness of the outer wall 120 is not critical, but isthin enough so that the central lumen 118 can accommodate one or morelead wires and any other desired wires, cables or tubes. If desired, theinner surface of the outer wall 120 is lined with a stiffening tube 121to provide improved torsional stability. In on embodiment, the outerwall 120 with an outer diameter of from about 0.090 inches to about0.094 inches and an inner diameter of from about 0.061 inches to about0.065 inches.

The catheter body 112, i.e., that portion that can be inserted into thepatient, can vary as desired. Preferably, the length ranges from about110 cm to about 120 cm. The distal region 114 on which the electrodes 71and 70 are mounted ranges in length from about 7.0 cm to about 15 cm,preferably about 8.0 cm to about 10 cm.

The ring electrodes 70 are preferably spaced apart from each other suchthat the electrodes span substantially the entire length of the distalregion 114 of the catheter body 112. The tip electrode 71 is mounted onthe distal end of the catheter body 112. However, a plurality of mappingelectrodes is preferred in order to ensure accurate determination of thelocation of the catheter EC relative to the heart catheter HC. The ringelectrodes and/or the tip electrode may be formed, at least in part, ofa radiopaque material to aid in the alignment, under fluoroscopy, of theelectrodes along the posterior wall of the left atrium.

Each ring electrode 70 and the tip electrode 71 is connected to acorresponding lead wire 150. The distal end of each lead wire 150 isattached to the corresponding electrode. The proximal end of each leadwire 150 is electrically connected to the SPU 34, where the electricalsignals received from the electrodes are analyzed with reference to theelectrical proximity signals generated by the signal generator 80 todetermine the proximity between the catheters as a means to monitor thedistance between the distal tip of the heart catheter HC and thesuperior wall 13 of the esophagus. As understood by one of ordinaryskill in the art, the electrodes of the esophagus catheter may receiveor transmit proximity signals, and the electrodes of the heart cathetermay correspondingly transmit or receive proximity signals.

As shown in FIG. 3, the lead wires 150 are enclosed within a protectivesheath 162 to prevent contact with other components within the lumen ofthe catheter body 112. The protective sheath 162 can be made of anysuitable material, preferably polyimide. The protective sheath 162 isanchored at its distal end to the proximal end of the catheter body 112by gluing it to the side wall of the catheter body 112 with polyurethaneglue or the like. As would be recognized by one of ordinary skill in theart, the protective sheath 162 can be eliminated if desired.

One or more temperature sensors may be provided in the distal region 114of the catheter body 112 to monitor the temperature of the esophagealtissue. Monitoring the temperature of the esophageal tissue allows thephysician to control power delivery during ablation with the heartcatheter HC in order to prevent thermal damage to the esophagus.

Any conventional temperature sensors, e.g. thermocouples or thermistors,may be used. In the embodiment shown in FIGS. 3 a and 3 c, thetemperature sensors comprise thermocouples formed by enameled wirepairs. One wire of each wire pair is a copper wire 153, e.g., a number40 copper wire. The other wire of each wire pair is a constantan wire154. The wires 153 and 154 of each wire pair are electrically isolatedfrom each other except at their distal ends where they are twistedtogether, covered with a short piece of plastic tubing 155, e.g.,polyimide, and covered with epoxy. The plastic tubings 155 are anchoredto the side wall of the catheter body 112 by glue or the like. Thetemperature sensors may be anchored anywhere along the length of thecatheter body 112, such that the temperature of the esophageal tissuecan be monitored. The wires 153 and 154 extend through the central lumen118 of the catheter body and out to a connector (not shown) connectableto a temperature monitor (not shown). As noted above with respect to thelead wires 150, the wires 153 and 154 may be encased within a protectivesheath 162, which can be made of any suitable material, preferablypolyimide. The protective sheath 162 is anchored at its distal end tothe side wall of the catheter body 112 by gluing it to the side wallwith polyurethane glue or the like.

An electromagnetic sensor 174 may be contained within the distal end ofthe esophagus catheter EC. The electromagnetic sensor 174 is mounted tothe side wall of the catheter body 112 by any suitable means, e.g., bypolyurethane glue or the like. The electromagnetic sensor 174 may beused to ensure that the distal end of the catheter EC is positioned inthe esophagus at a location below the left atrium of the heart.Positioning the tip of the catheter EC generally below the left atriumensures that the plurality of ring electrodes 70 on the distal region114 are aligned along the posterior wall of the left atrium, and thatthe electrodes 70 and 71 span substantially the length of the posteriorleft atrial wall. The electromagnetic sensor 174 may also be used todetermine the proximity of the esophagus to the heart catheter HC, asdiscussed further below.

The electromagnetic sensor 174 is connected to an electromagnetic sensorcable 175, which extends through the central lumen 118 of the catheterbody 112, and out through the electrical connector 37. Theelectromagnetic sensor cable 175 comprises multiple wires encased withina plastic covered sheath. The PIU 24 amplifies the signal received fromthe electromagnetic sensor 174 and transmits it to the COM unit 20.Because the catheter EC is designed for a single use only, the circuitboard may contain an EPROM chip which shuts down the circuit boardapproximately 24 hours after the catheter has been used. This preventsthe catheter, or at least the electromagnetic sensor from being usedtwice. Suitable electromagnetic sensors for use with the presentinvention are described, for example, in U.S. Pat. Nos. 5,558,091,5,443,489, 5,480,422, 5,546,951 and 5,391,199, the entire disclosures ofwhich are incorporated herein by reference.

As discussed above, the SPU 34 analyzes the electrical signals receivedfrom the electrodes of the esophagus catheter EC and the heart catheterHC. Once analyzed, the SPU 34 generates a signal to alert the physicianto the proximity of the esophagus to the distal tip region of the heartcatheter HC. In one embodiment, the SPU 34 analyzes the signals throughimpedance measurement. Using this technique, the impedance between theelectrodes on the esophagus catheter and those on the heart catheter iscontinuously measured. A decrease in impedance between the two cathetersindicates that the electrode(s) on the heart catheter is close to theesophagus. In one embodiment, when the impedance measurement drops belowa predetermined threshold value, the physician is alerted that theelectrode(s) of the heart catheter is too close to the esophagus.

In an alternative embodiment, pacing signal amplitude measurement isused to measure the proximity of the ablation electrode(s) to theesophagus. Using this technique, a pacing signal is sent to theelectrodes on the esophagus probe catheter EC and is detected by theelectrode(s) on the heart catheter HC. As the two catheters come intoproximity of each other, the amplitude of the pacing signal increases,indicating that the electrode(s) of the heart catheter HC are close tothe esophagus. When the amplitude of the pacing signal rises above athreshold value, the physician is alerted that the electrode(s) of theheart catheter HC are too close to the esophagus.

In yet another embodiment, a magnetic field may be used to determine theproximity of the ablation electrode(s) to the esophagus. Using thistechnique, both the catheters EC and HC comprise electromagneticsensors. With the magnetic fields generated by the location pad 22, theelectromagnetic sensors of the catheters generate electrical signalsindicative of their location within the magnetic fields. This locationalinformation enables the physician to determine the proximity of theablation electrode(s) to the esophagus. Other suitable techniques fordetermining the proximity of the ablation electrode to the esophagusinclude inductance measurement, capacitance measurement and the use ofHall effect sensors.

In use, the esophagus catheter EC is inserted into the esophagus of apatient. The esophagus catheter may guided into the esophagus underfluoroscopy to align the electrodes along the posterior left atrial wall14. The esophagus catheter EC remains in the esophagus for the durationof the catheter-based endocardial procedure. Before or after placementof the esophagus catheter EC, the heart catheter HC is inserted into theleft atrium of the patient's heart, and tissue in the left atrium ismapped and/or ablated using the at least one electrode of the heartcatheter. During the endocardial procedure, at least one electrode ofone catheter transmits a proximity signal to at least one electrode ofthe other catheter. The SPU 34 compares the signals at the electrodes ofthe two catheters to determine the proximity of the catheters andgenerates a signal to inform, if not alert, the physician of theproximity. The system monitors the proximity on a continuous, real-timebasis during the endocardial procedure.

The preceding description has been presented with reference to presentlypreferred embodiments of the invention. Workers skilled in the art andtechnology to which this invention pertains will appreciate thatalterations and changes to the described structure may be practicedwithout meaningfully departing from the principal, spirit and scope ofthis invention. Accordingly, the foregoing description should not beread as pertaining only to the precise structures described andillustrated in the accompanying drawings, but rather should be readconsistent with and as support for the following claims which are tohave their fullest and fairest scope.

1. A method of monitoring proximity between a heart catheter positionedin a patient's heart and the patient's esophagus, comprising:positioning an esophagus catheter having a closed distal end to remainin the patient's esophagus; positioning a heart catheter in thepatient's heart a distance from the esophagus catheter; transmitting aproximity signal between the esophagus catheter and the heart catheter,wherein the proximity signal is transmitted through cardiac tissue andesophageal tissue; determining a proximity between the catheters bymonitoring a characteristic of the proximity signal indicative of theproximity between the catheters; and triggering an audio and/or visualsignal to a user when the proximity between the catheters reaches apredetermined proximity.
 2. A method of claim 1, wherein thecharacteristic is impedance.
 3. A method of claim 1, wherein thecharacteristic is amplitude.
 4. A method of claim 1, wherein thecharacteristic is phase.